1. Field of the Invention
The present invention relates to a method and a device for the purification of fluids, especially water, which is part of, among other things, closed and open water-based heating and cooling plants, ice water plants, district heating plants, heat recovery plants, open cooling towers, etc., by preferably continuous partial flow filtration. The method and fluid purification device according to the invention also include the purification of new fluid for the water-based heating/cooling plant etc., before supplying or recharging into the plant in question, and also the purification of filtering media and possible other media which are comprised by the fluid filtration device.
2. Description of the Prior Art
The knowledge of water treatment is a highly specialized science, in which the effort, in Norway, has been concentrated mainly on securing the intake and transport of consumption water to the consumers. The requirements to quality and properties of water have until the last 5-6 years been connected to medical conditions, including the use of chlorine to inactivate harmful bacteria, micro organisms etc. Only in the recent years parameters like alkalinity, calcium content and pH have been thought to be of major importance. Norway is one of the few European countries in which so-called surface water is used, that is water from open resources like dams, tarns, brooks, inland water, lakes or similar. This water type is very poor in dissolved minerals, metals and salts. The water type has a low electric conductivity, normal pH value of 4-6, i.e. acid surplus, and is characterized as soft, i.e. almost without any calcium and magnesium. These are water properties clearly distinguishing surface water form the properties of groundwater which, among other things, is richer in minerals.
As carrier of energy, carrier of thermal energy--heat or cold carrier--water has a series of properties making it unique in the field of chemistry.
As know, water can be found in three different phases: as ice, in the form of liquid and in the form of gas (as vapour). In the liquid state not other liquid has a greater ability and capacity of absorbing, retaining and emitting thermal energy.
In the earliest centrally heated heating plants there was no use of centrifugal pumps, the introduction of which reduced the installation investments, which made central heating and water-based energy transfer more easily available to a considerably larger amount of consumers than before.
A number of serious problems have been encountered in water-based heating plants, cooling towers etc. In countries having water sources based on ground water sedimentation problems quickly developed in closed heating systems, which resulted in a great increase in the consumption of energy. Internal sedimentation from ground water mainly consists of lime (calcium) and magnesium, which is kept dissolved in the water as long as the content of aggressive carbonic acid is sufficient. However, this carbonic acid content is reduced as the ground water is being pumped to the surface, and by heating, whereby the lime and the magnesium passes from the dissolved to the solid state, followed by desimentation on the hottest surfaces. Such sedimentation results in greatly reduced heat transfer capacity in for example the boiler of a heating plant, which may have serious consequences: increased energy consumption to operate the plant, possible production interruptions, and a risk of destruction of material and accidents among the staff.
These sedimentation/deposit problems were sought to be solved by reducing the pH value to thereby keep said minerals in the dissolved state. However, this required the use of very low pH values, so that in stead substantial acidic corrosion problems arose.
However, the introduction of phosphorus compounds very effectively solved the sedimentation problems by keeping calcium and magnesium in the dissolved state in a wide temperature range, without introducing other problems such as deposits or corrosion in the plant. The use of these phosphorus compounds quickly become so commonly used that, also in countries having surface water of low pH value, these additives were added uncritically to water for heating/cooling plants, without the water first being submitted to a detailed examination or chemical analysis to prove the need for such additives.
A conventional heating/cooling plant etc. has an outer piping circuit which together with the plant form a closed loop and in which a circulation pump is connected in a well known manner. A partial flow of the water circulating in the heating/cooling plant and in the outer circuit, is drawn from the circuit at a bleeding point in the pipe circuit, and is lead through a further pipe, having an in-line shut-off valve, to a filtration housing containing a filter mass for mechanical filtration of the water, which thereafter, possibly together with recharge water, is returned to the circuit through a return pipe with a control valve. The filter mass in the filtration housing must be replaced frequently. The filtration effect is not very satisfactory, both in terms of quality and quantity.